4. Verb tense and voice

4.1
Present tense

Use thepresent tense for statements of fact and general truths, for a set of steps in a method (not for the specific steps used when
testing or gathering data published in the paper), and for any results, discussion, and conclusions that are set out in the paper itself.

Time markers for the present include “now”, “usually”, “often”, “currently”, “at present”, but the context will also indicate the time frame.

In the usual reduction procedure, data are flux-calibrated and dereddened.

Our data were then flux-calibrated and dereddened. (Specific actions taken and completed in the past.)

As opposed to the “present simple”, there is seldom need for the present continuous (progressive) in science writing, since the work was done earlier, not
while actually writing. One exception might be if you are describing an ongoing project that began before and continues after the time of writing.

“You are not simulating and getting the results right now.”

“The satellite’s spectrometer is measuring….in orbit.”

“When assuming trailing spiral arms, the northwestern side of the nebula is nearest to us, and the galaxy is rotating counter-clockwise.” (“rotates” is
correct, too.)

4.2 Present simple and present perfect

The present simple and present perfect are both used to refer to what is said by others in their papers, but what they did in the research itself can be in
the simple past, as explained below. Avoid using the present for your work and the past tense for others’ work in a paper, because it may suggest that
theirs is not correct or out of date.

We can accept the simple past for what is said in papers from 2000 and earlier, but that is not the usual English convention for anything said in a book or
article.

Time markers
for the present perfect include “just”, “recently”, “already”, “ever”, “never”, “since” with a precise date, “for” with a time duration up to the present.

“Smith et al. (2010) [have] studied… They conclude that… We did a similar study.”

4.3
Simple past vs present perfect

The simple past is used for events that occurred and were completed in the past, whereas thepresent perfect implies a continuation into
the present of that action or a recent change that has a connection with or is important in the present: e.g., “I now explain the new technique that has
been developed.” (developed in the past but important now because being explained).

In a research paper, the past is used for your actions (e.g., research) that were completed before writing began (observations, calculations, tests of
models), so this tense is appropriate for the methods sections of the abstract and paper. You also need to use it for the summaries of what is said earlier
in a paper, making it appropriate in the last section.

Time markers
for the simple past include any phrase that indicates a past and finished time or time period: “In 2009, we observed…”, “Five years ago, we presented this
idea at a colloquium in…” The context may also indicate an action completed in the past.

“This paper has shown that…”

This can begin the summary section, but subsequent sentences for what was done in the paper should be in the simple past, with a few exceptions, especially
in UK English: “We have investigated…Our analysis proved…We discussed…” All the results, in contrast, are given in the present tense.

4.4
Alternating tenses

You may move between tenses, when needed, but the change in time frame must be made clear by a change in situation or by a ``time marker”, that is, a
phrase to indicate a switch in time frame (underlined in the example below, which was adapted from p. 77 of Minimum Competence in Scientific English, nouvelle édition, by S. Blattes et al., Grenoble Sciences and EDP Sciences, 2003).

Example:
“The Hubble deep field consists of 300 images that were takenin 1995. It maps just one small… Never beforehave so much data been available.”

4.5
Future

The future is expressed in English with either the present simple or the verb “will” and the base form (infinitive without “to”). When referring to work
that follows in the same paper, use the present to describe the immediate and certain future: “We explain our method in Sect. 2.”

For future work after this article or for predicted events, use the future form with “will”.

“Once these stars have been observed, they will be analyzed with the new method.”

N.B. In the subjunctive (conditional) use of “will”, neither “will” nor “would” is used after the subordinating conjunction:

“If we will take two nights to observe, we will be able to detect the source.”

“If we take two nights to observe, we will be able to detect the source.”

“If Galileo had not withdrawn his claims, he would have been burned.” or

“Had Galileo not withdrawn…”

4.6
Active vs passive voice

Unlike the active voice, the passive voice emphasizes a process or event leading to results more than the actor, so science writing tends to use the
passive, especially when there are large teams of researchers. However, this leads to wordy and often complex sentences and paragraphs when used
exclusively, so A&A recommends more use of the active or at least asks for the voice to be varied in all sections of the paper.

Example:
“That such observations can lead to accurate results is demonstrated by our analysis” should be written as “Our analysis demonstrates that such
observations lead to accurate results.”

4.7
Multiword verb phrases

Verbal phrases sometimes cause problems in papers. Some of them require a specific adjective or preposition, or the meaning changes with that additional
word (Compare “break down”, “break off”, and “break out”). See Sect. 8 for several examples of the verb phrases we see most often: “depend on” or
“associate with”.

Other multiword verbs require that the additional words go after any direct object and are called “separable”: “to take something into account”.

4.8
Gerunds and infinitives

Gerunds and infinitives are used with different verbs, and when one verb takes either form, then something different may be implied. This is also true for
reported speech.

Verb+ing (gerund or present participle): “They suggested taking more time for the observations.” These verbs include “admit”, “anticipate”,
“consider”, “finish”, “mention”, “propose”, “recall”, “recommend”, “remember”, “report”, “suggest”. In this list, only “finish” cannot also be used
with a “that” clause.

Example:
“We recall seeing it there” or “We recall that we saw it there.”

There are other phrases where the gerund or infinitive can be used but with different meanings.

Example:
“We stopped doing that” means we ceased doing it, but “We stopped to do that” means you interrupted another action to do it.